Sodium Channel Blockers

The effect of sodium channels on neurological/neuronal disorders: A systematic review

Neurological and neuronal disorders are associated with structural, biochemical, or electrical abnormalities in the nervous system. Many neurological diseases have not yet been discovered. Interventions used for the treatment of these disorders include avoidance measures, lifestyle changes, physiotherapy, neurorehabilitation, pain management, medication, and surgery. In the sodium channelopathies, alterations in the structure, expression, and function of voltage-gated sodium channels (VGSCs) are considered as the causes of neurological and neuronal diseases. Online databases, including Scopus, Science Direct, Google Scholar, and PubMed were assessed for studies published between 1977 and 2020 using the keywords of review, sodium channels blocker, neurological diseases, and neuronal diseases. VGSCs consist of one α subunit and two β subunits. These subunits are known to regulate the gating kinetics, functional characteristics, and localization of the ion channel. These channels are involved in cell migration, cellular connections, neuronal pathfinding, and neurite outgrowth. Through the VGSC, the action potential is triggered and propagated in the neurons. Action potentials are physiological functions and passage of impermeable ions. The electrophysiological properties of these channels and their relationship with neurological and neuronal disorders have been identified. Subunit mutations are involved in the development of diseases, such as epilepsy, multiple sclerosis, autism, and Alzheimer's disease. Accordingly, we conducted a review of the link between VGSCs and neurological and neuronal diseases. Also, novel therapeutic targets were introduced for future drug discoveries.

Machine learning-based QSAR models to predict sodium ion channel (Nav 1.5) blockers

Aim: Conventional experimental approaches used for the evaluation of the proarrhythmic potential of compounds in the drug discovery process are expensive and time consuming but an integral element in the safety profile required for a new drug to be approved. The voltage-gated sodium ion channel 1.5 (Na_v 1.5), a target known for arrhythmic drugs, causes adverse cardiac complications when the channel is blocked. Results: Machine learning classification and regression models were built to predict the possibility of blocking these channels by small molecules. The finalized models tested with balanced accuracies of 0.88, 0.93 and 0.94 at three thresholds (1, 10 and 30 µmol, respectively). The regression model built to predict the pIC₅₀ of compounds had q² of 0.84 (root-mean-square error = 0.46). Conclusion: The machine learning models that have been built can act as effective filters to screen out the potentially toxic compounds in the early stages of drug discovery.

Aspartic Acid Isomerization Characterized by High Definition Mass Spectrometry Significantly Alters the Bioactivity of a Novel Toxin from Poecilotheria

Research in toxinology has created a pharmacological paradox. With an estimated 220,000 venomous animals worldwide, the study of peptidyl toxins provides a vast number of effector molecules. However, due to the complexity of the protein-protein interactions, there are fewer than ten venom-derived molecules on the market. Structural characterization and identification of post-translational modifications are essential to develop biological lead structures into pharmaceuticals. Utilizing advancements in mass spectrometry, we have created a high definition approach that fuses conventional high-resolution MS-MS with ion mobility spectrometry (HDMSE) to elucidate these primary structure characteristics. We investigated venom from ten species of "tiger" spider (Genus: Poecilotheria) and discovered they contain isobaric conformers originating from non-enzymatic Asp isomerization. One conformer pair conserved in five of ten species examined, denominated PcaTX-1a and PcaTX-1b, was found to be a 36-residue peptide with a cysteine knot, an amidated C-terminus, and isoAsp33Asp substitution. Although the isomerization of Asp has been implicated in many pathologies, this is the first characterization of Asp isomerization in a toxin and demonstrates the isomerized product's diminished physiological effects. This study establishes the value of a HDMSE approach to toxin screening and characterization.

N-Guanidyl and C-Tetrazole Leu-Enkephalin Derivatives: Efficient Mu and Delta Opioid Receptor Agonists with Improved Pharmacological Properties

Leu-enkephalin and d-Ala₂-Leu-enkephalin were modified at their N- and C-termini with guanidyl and tetrazole groups. The resulting molecules were prepared in solution or by solid phase peptide synthesis. The affinity of the different analogues at mu (MOP) and delta opioid receptors (DOP) was then assessed by competitive binding in stably transfected DOP and MOP HEK293 cells. Inhibition of cAMP production and recruitment of β-arrestin were also investigated. Finally, lipophilicity (logD_7.4) and plasma stability of each compound were measured. Compared to the native ligands, we found that the replacement of the terminal carboxylate by a tetrazole slightly decreased both the affinity at mu and delta opioid receptors as well as the half-life. By contrast, replacing the ammonium at the N-terminus with a guanidyl significantly improved the affinity, the potency, as well as the lipophilicity and the stability of the resulting peptides. Replacing the glycine residue with a d-alanine in position 2 consistently improved the potency as well as the stability of the analogues. The best peptidomimetic of the whole series, guanidyl-Tyr-d-Ala-Gly-Phe-Leu-tetrazole, displayed sub-nanomolar affinity and an increased lipophilicity. Moreover, it proved to be stable in plasma for up to 24 h, suggesting that the modifications are protecting the compound against protease degradation.

Autism throughout genetics: Perusal of the implication of ion channels

BACKGROUND

Autism spectrum disorder (ASD) comprises a group of neurodevelopmental psychiatric disorders characterized by deficits in social interactions, interpersonal communication, repetitive and stereotyped behaviors and may be associated with intellectual disabilities. The description of ASD as a synaptopathology highlights the importance of the synapse and the implication of ion channels in the etiology of these disorders.

METHODS

A narrative and critical review of the relevant papers from 1982 to 2017 known by the authors was conducted.

RESULTS

Genome-wide linkages, association studies, and genetic analyses of patients with ASD have led to the identification of several candidate genes and mutations linked to ASD. Many of the candidate genes encode for proteins involved in neuronal development and regulation of synaptic function including ion channels and actors implicated in synapse formation. The involvement of ion channels in ASD is of great interest as they represent attractive therapeutic targets. In agreement with this view, recent findings have shown that drugs modulating ion channel function are effective for the treatment of certain types of patients with ASD.

CONCLUSION

This review describes the genetic aspects of ASD with a focus on genes encoding ion channels and highlights the therapeutic implications of ion channels in the treatment of ASD.

Comparison of permeation mechanisms in sodium-selective ion channels

Voltage-gated sodium channels are the molecular components of electrical signaling in the body, yet the molecular origins of Na⁺-selective transport remain obscured by diverse protein chemistries within this family of ion channels. In particular, bacterial and mammalian sodium channels are known to exhibit similar relative ion permeabilities for Na⁺ over K⁺ ions, despite their distinct signature EEEE and DEKA sequences. Atomic-level molecular dynamics simulations using high-resolution bacterial channel structures and mammalian channel models have begun to describe how these sequences lead to analogous high field strength ion binding sites that drive Na⁺ conduction. Similar complexes have also been identified in unrelated acid sensing ion channels involving glutamate and aspartate side chains that control their selectivity. These studies suggest the possibility of a common origin for Na⁺ selective binding and transport.

Understanding Sodium Channel Function and Modulation Using Atomistic Simulations of Bacterial Channel Structures

Sodium channels are chief proteins involved in electrical signaling in the nervous system, enabling critical functions like heartbeat and brain activity. New high-resolution X-ray structures for bacterial sodium channels have created an opportunity to see how these proteins operate at the molecular level. An important challenge to overcome is establishing relationships between the structures and functions of mammalian and bacterial channels. Bacterial sodium channels are known to exhibit the main structural features of their mammalian counterparts, as well as several key functional characteristics, including selective ion conduction, voltage-dependent gating, pore-based inactivation and modulation by local anesthetic, antiarrhythmic and antiepileptic drugs. Simulations have begun to shed light on each of these features in the past few years. Despite deviations in selectivity signatures for bacterial and mammalian channels, simulations have uncovered the nature of the multiion conduction mechanism associated with Na(+) binding to a high-field strength site established by charged glutamate side chains. Simulations demonstrated a surprising level of flexibility of the protein, showing that these side chains are active participants in the permeation process. They have also uncovered changes in protein structure, leading to asymmetrical collapses of the activation gate that have been proposed to correspond to inactivated structures. These observations offer the potential to examine the mechanisms of state-dependent drug activity, focusing on pore-blocking and pore-based slow inactivation in bacterial channels, without the complexities of inactivation on multiple timescales seen in eukaryotic channels. Simulations have provided molecular views of the interactions of drugs, consistent with sites predicted in mammalian channels, as well as a wealth of other sites as potential new drug targets. In this chapter, we survey the new insights into sodium channel function that have emerged from studies of simpler bacterial channels, which provide an excellent learning platform, and promising avenues for mechanistic discovery and pharmacological development.

IonWorks Barracuda Assay for Assessment of State-Dependent Sodium Channel Modulators

Voltage-gated sodium channels represent important drug targets. The implementation of higher throughput electrophysiology assays is necessary to characterize the interaction of test compounds with several conformational states of the channel, but has presented significant challenges. We describe a novel high throughput approach to assess the effects of test agents on voltage-gated sodium currents. The multiple protocol mode of the automated electrophysiology instrument IonWorks Barracuda was used to control the level of inactivation and monitor current stability. Good temporal stability of currents and spatial uniformity of inactivation were obtained by optimizing the experimental conditions. The resulting assay allowed for robust assessment of state-dependent effects of test agents and enabled direct comparison of compound potency across several sodium channel subtypes at equivalent levels of inactivation.

Ion channels as drug targets in central nervous system disorders

Ion channel targeted drugs have always been related with either the central nervous system (CNS), the peripheral nervous system, or the cardiovascular system. Within the CNS, basic indications of drugs are: sleep disorders, anxiety, epilepsy, pain, etc. However, traditional channel blockers have multiple adverse events, mainly due to low specificity of mechanism of action. Lately, novel ion channel subtypes have been discovered, which gives premises to drug discovery process led towards specific channel subtypes. An example is Na(+) channels, whose subtypes 1.3 and 1.7-1.9 are responsible for pain, and 1.1 and 1.2 - for epilepsy. Moreover, new drug candidates have been recognized. This review is focusing on ion channels subtypes, which play a significant role in current drug discovery and development process. The knowledge on channel subtypes has developed rapidly, giving new nomenclatures of ion channels. For example, Ca(2+)s channels are not any more divided to T, L, N, P/Q, and R, but they are described as Ca(v)1.1-Ca(v)3.3, with even newer nomenclature α1A-α1I and α1S. Moreover, new channels such as P2X1-P2X7, as well as TRPA1-TRPV1 have been discovered, giving premises for new types of analgesic drugs.

Design and assessment of a potent sodium channel blocking derivative of mexiletine for minimizing experimental neuropathic pain in several rat models

Physical or chemical damage to peripheral nerves can result in neuropathic pain which is not easily alleviated by conventional analgesic drugs. Substantial evidence has demonstrated that voltage-gated Na+ channels in the membrane of damaged nerves play a key role in the establishment and maintenance of pathological neuronal excitability not only of these peripheral nerves but also in the second- and third-order neurons in the pain pathway to the cerebral cortex. Na+ channel blocking drugs have been used in treating neuropathic pain with limited success mainly because of a preponderance of side-effects. We have developed an analogue of mexiletine which is approximately 80 times more potent than mexiletine in competing with the radioligand, 3H-batrachotoxinin for binding to Na+ channels in rat brain membranes and also it is much more lipophilic than mexiletine which should enhance its uptake into the brain to block the increased expression of Na+ channels on second- and third-order neurons of the pain pathway. This analogue, HFI-1, has been tested in three different rat models of neuropathic pain (formalin paw model, ligated spinal nerve model and contusive spinal cord injury model) and found to be more effective in reducing pain behaviours than mexiletine.

Neuromuscular disease in the dialysis patient: an update for the nephrologist

Neuromuscular disease is an extremely common complication of end-stage kidney disease (ESKD), manifesting in almost all dialysis patients, and leading to weakness, reduced exercise capacity, and disability. Recent studies have suggested that hyperkalemia may underlie the development of neuropathy. As such, maintenance of serum K(+) within normal limits between periods of dialysis in ESKD patients manifesting early neuropathic symptoms may reduce neuropathy development and progression. For patients with more severe neuropathic syndromes, increased dialysis frequency or a switch to high-flux dialysis may prevent further deterioration, while ultimately, renal transplantation is required to improve and restore nerve function. Exercise training programs are beneficial for ESKD patients with muscle weakness due to neuropathy or myopathy, and are capable of improving exercise tolerance and quality of life. Specific treatments have recently been evaluated for symptoms of autonomic neuropathy, including sildenafil for impotence and midodrine for intra-dialytic hypotension, and have been shown to be effective and well tolerated. Other important management strategies for neuropathy include attention to foot care to prevent callus and ulceration, vitamin supplementation, and erythropoietin. Treatment with membrane-stabilizing agents, such as amitryptiline and gabapentin, are highly effective in patients with painful neuropathy.

The discovery of a selective, small molecule agonist for the MAS-related gene X1 receptor

The novel 7-transmembrane receptor MrgX1 is located predominantly in the dorsal root ganglion and has consequently been implicated in the perception of pain. Here we describe the discovery and optimization of a small molecule agonist and initial docking studies of this ligand into the receptor in order to provide a suitable lead and tool compound for the elucidation of the physiological function of the receptor.

The pharmacology of voltage-gated sodium channels in sensory neurones

Voltage-gated sodium channels (VGSCs) are vital for the normal functioning of most excitable cells. At least nine distinct functional subtypes of VGSCs are recognized, corresponding to nine genes for their pore-forming alpha-subunits. These have different developmental expression patterns, different tissue distributions in the adult and are differentially regulated at the cellular level by receptor-coupled cell signalling systems. Unsurprisingly, VGSC blockers are found to be useful as drugs in diverse clinical applications where excessive excitability of tissue leads to pathological dysfunction, e.g. epilepsy or cardiac tachyarrhythmias. The effects of most clinically useful VGSC blockers are use-dependent, i.e. their efficacy depends on channel activity. In addition, many natural toxins have been discovered that interact with VGSCs in complex ways and they have been used as experimental probes to study the structure and function of the channels and to better understand how drugs interact with the channels. Here we have attempted to summarize the properties of VGSCs in sensory neurones, discuss how they are regulated by cell signalling systems and we have considered briefly current concepts of their physiological function. We discuss in detail how drugs and toxins interact with archetypal VGSCs and where possible consider how they act on VGSCs in peripheral sensory neurones. Increasingly, drugs that block VGSCs are being used as systemic analgesic agents in chronic pain syndromes, but the full potential for VGSC blockers in this indication is yet to be realized and other applications in sensory dysfunction are also possible. Drugs targeting VGSC subtypes in sensory neurones are likely to provide novel systemic analgesics that are tissue-specific and perhaps even disease-specific, providing much-needed novel therapeutic approaches for the relief of chronic pain.

The pitfalls of profoundly effective analgesic therapies

OBJECTIVE

In essentially all areas of pain medicine, treatments with improved effectiveness are needed. Though gains have been made in recent years, suffering from acute postoperative pain, low back pain, cancer-related pain, and pain from other causes remains problematic. On the other hand, both science and industry are approaching the problem with ever more sophisticated techniques. Though not currently in our armamentarium, it seems likely that at some point we will be faced with the situation where profoundly effective broad-spectrum analgesic therapies are available to our patients. Depending on their mechanisms of action, there may be significant downsides to the use of these new medications. The objective of this report was to explore the consequences of developing profoundly effective analgesic agents.

METHODS

This report reviews some of the recent advancements in our march toward developing profoundly effective analgesics and some of the pitfalls we might anticipate will be associated with these agents. Specifically, the issue of pain as an essential protective mechanism is explored. The causes and consequences of inherited neuropathies associated with pain insensitivity are reviewed.

RESULTS

The ability to appreciate internal and external stimuli as painful is critical to humans. The loss of this ability has profound adverse consequences which in their extreme can be life threatening. Significant social issues might arise from the availability of profoundly effective analgesics. A structure for managing the introduction of these agents into clinical practice is suggested.

DISCUSSION

By anticipating the likely clinical properties of profoundly effective analgesics we place ourselves in best position to guide their development, assure their safety, and oversee their use. The early collaboration of industry, scientists, clinicians, and regulatory authorities may be the best course.

Pregabalin in the treatment of neuropathic pain associated with diabetic peripheral neuropathy

Neuropathic pain associated with diabetic peripheral neuropathy (DPN) is a common debilitating complication of diabetes mellitus with unmet therapeutic needs. Pregabalin is a recently introduced α2-δ subunit ligand at the voltage- sensitive calcium channel that has shown good efficacy with a tolerable side-effect profile in the treatment of PDN. According to the Australian datasheet, 1438 patients have been studied receiving either placebo (460) or pregabalin (978). The dose ranged from 75 to 600 mg daily. The number needed to treat averaged from the published data is 3.8 patients for the two higher doses. Pregabalin has a linearly increased plasma concentration with dose escalation and achieves analgesia as early as 1 day after initiating therapy. As its mechanism of action is different from other anticonvulsants and antidepressants, and interactions with other drugs are unlikely from the pharmacokinetic profile, combining pregabalin with other agents that are effective in DPN is a clinically safe option and should result in improved pain control.

Discovery of potent furan piperazine sodium channel blockers for treatment of neuropathic pain

The synthesis and pharmacological characterization of a novel furan-based class of voltage-gated sodium channel blockers is reported. Compounds were evaluated for their ability to block the tetrodotoxin-resistant sodium channel Na(v)1.8 (PN3) as well as the Na(v)1.2 and Na(v)1.5 subtypes. Benchmark compounds from this series possessed enhanced potency, oral bioavailability, and robust efficacy in a rodent model of neuropathic pain, together with improved CNS and cardiovascular safety profiles compared to the clinically used sodium channel blockers mexiletine and lamotrigine.

Discovery and biological evaluation of 5-aryl-2-furfuramides, potent and selective blockers of the Nav1.8 sodium channel with efficacy in models of neuropathic and inflammatory pain

Nav1.8 (also known as PN3) is a tetrodotoxin-resistant (TTx-r) voltage-gated sodium channel (VGSC) that is highly expressed on small diameter sensory neurons and has been implicated in the pathophysiology of inflammatory and neuropathic pain. Recent studies using an Nav1.8 antisense oligonucleotide in an animal model of chronic pain indicated that selective blockade of Nav1.8 was analgesic and could provide effective analgesia with a reduction in the adverse events associated with nonselective VGSC blocking therapeutic agents. Herein, we describe the preparation and characterization of a series of 5-substituted 2-furfuramides, which are potent, voltage-dependent blockers (IC50 < 10 nM) of the human Nav1.8 channel. Selected derivatives, such as 7 and 27, also blocked TTx-r sodium currents in rat dorsal root ganglia (DRG) neurons with comparable potency and displayed >100-fold selectivity versus human sodium (Nav1.2, Nav1.5, Nav1.7) and human ether-a-go-go (hERG) channels. Following systemic administration, compounds 7 and 27 dose-dependently reduced neuropathic and inflammatory pain in experimental rodent models.